Coralline Crag

Coralline Crag, a series of sands containing numerous calcareous fossils, especially Polyzoa, and having a thickness of from 40 to 60 feet, which form the base of the Pliocene series in Suffolk. It is also known as the Suffolk, White, or Bryozoan Crag, as it resembles chalk in appearance, and the prevailing group of fossils in it are not corallines (q.v.), but Polyzoa or, as they are sometimes called, Bryozoa. At the base of the series is the Suffolk bone-bed, from six inches to three feet thick, containing phosphatic nodules and water-worn teeth and bones of Mastodon, Rhinoceros, tapir, bear, whales, and sharks, together with rounded sandstone concretions, called "box-stones." The Coralline Crag is believed to have been deposited in a sea not more than 300 feet deep. It has yielded 140 species of Polyzoa; and of the Mollusca 84 per cent. are living species, and 5 per cent. are northern types.